Parts for machinery



March 5, 1957 E. SORENSEN PARTS FOR MACHINERY Filed Sept. 8, 1949 INVENTOR EMIL- s6RENsEN ATTORNEYS United States 7 Claims. Cl. 253-77 This invention relates to certain improvements in regard to parts for machinery, more particularly, vanes for exhaust gas turbines, made from ceramic material.

It has been heretofore suggested to make various parts for machinery, exposed to high service temperatures, from ceramic material owing to the considerable strength at elevated temperature of some ceramic masses combined with low specific gravity. However, in many instances, in addition to this property a rather high stability against change of temperature is required in order to ensure safe operation in case of rapid changes of thethermal conditions. It is very diflicult, however, to find a material which combines a maximum of both of said, required characteristics, since in most instances a maximum of one of said characteristics is combined with a minimum of the other characteristic, while favorable. properties in both respects are required for some machine parts which are exposed to high mechanical and. thermal stresses. For instance, owing to the centrifugal effect the stress in the blade portion of a turbine vane decreases constantly towards the tip of the blade while practically the same or even higher stresses occur at the T-shaped root of the vane by which the vane is connected to the rotor disc, owing to local increases of the stress at the points where the direction of the load is changing and owing to other influences of the shape and themachining. Therefore, it would be attempted, e, g., when casting the vanes, to obtain the densest shard or structure after the burning at the root portion of the vane, by a special shape of the mould, which as a rule means maximum strength. In this connection, also the application of the centrifugal casting process may bring an advantage. improvements will not be sufiicient substantially to increase the rated fatigue limit of a ceramic vane.

It is the object ofthe present invention to provide a structure of parts of the kind referred to by means of which it is possible to meet the said contradicting requirements.

The design of such parts of machinery according to the present invention is based on the fact that the requirements as to the various properties of the material are different for the various portions or elements of a machine part. Therefore, according to the present invention the constructional elements of a machine part exposed to different service conditions, e. g., the blade portion and the root portion of a turbine vane are made of dilferent ceramic materials with diiferent properties, i. e., a kind of compound or composite ceramic is created which will satisfy all demands required from the machine part. Taking the operating conditions into consideration, therefore, the root portion is made from a composition of the ceramic mass which primarily has a high strength at elevated temperature while the blade portion is made from a material which perhaps has a somewhat lower mechanical strength but a higher resistance against change of temperature.

Where the mass is cast in plaster molds, the slop of It is to be expected, however, that these atent high resistance against changes of temperature may be filled in first, removing the excess of the slop and filling in the slop of a composition of higher strength at elevated temperature when a certain thickness of the deposit has been reached at the inner walls of the mould. Since care must be taken in shaping the vane for high stresses (hi h average peripheral velocity in the pitch circle of the blade grid combined with a relatively long length of the blade) that the tapering in section of the blade portion is very considerable and that a gradual transition of the cross section from the blade to the thicker root portion is provided, the cross section of the core of high strength at elevated temperature will continuously increase in the shaft portion while forming the bulk of the load carrying cross section in the root portion which is stressed in the direction of several axes.

It will be understood thatthetwo materials should be so similar to each other as regards their physical properties that no additional forces are produced in the transition zone of the manufacture, by stresses, heating etc, which would cause bursting of the bond. A better transition Zone can be obtainedfby a gradual change of the slop from the one to the other composition as will be hereinafter described.

Otherand furtherobjects, features and advantages of the invention will be pointed out hereinafter and appear in the appended claims forming part of the application.

In the accompanying drawings several now preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

In'the drawings:

Fig. 1 is avvertical section, through a vane having the invention applied thereto.

Fig. 2 is a section on line II-Il in Fig. l.

Fig. 3 is a section on line Ill-J11 in Fig. l, and

Fig. 4 is a vertical section through a vane having the invention applied thereto but omitting the intermediate ceramic layer.

As will be seen from the drawing, the vane comprises a blade portion 4 and a root portion 5 and has an outer layer 1, an intermediate layer 2 and an inner layer 3 filling up theinner space left free by the layers 1 and 2. The inner layer or core 3 will consist of a material of a high mechanical strength at elevated temperature, such as steatite, while the outer layer 1 consists of a material of a high resistance against changes of temperature, such as, steatite with an addition of silicon carbide, e. g. in a proportion of 3 parts by weight of steatite and 1 part by weight of silicon carbide. The intermediate layer 2 may consist of a slop comprising 3 parts by weight of steatite and 0.5 part by weight of silicon carbide to obtain a smooth transition between the inner and outer slops 1 and 3. It is also possible, however, to do without said intermediate layer as indicated in Fig. 4, so that the whole free space left by the layer 11 is filled up by the core 13.

In practice, the structure shown in the drawing may be obtained in such a way that the slop 1 (e. g. 3 parts steatite, 1 part silicon carbide) is first filled into the plaster mould and allowed to form a deposit at the walls of the mould, as the moisture contained in the slop is absorbed by the plaster mould. When a layer of a sufiicient thickness has been formed, the remaining liquid slop is poured out and the hollow space is filled up with slop 2 (3 parts by Weight of steatite, 0.5 parts silicon carbide). Again, when a layer 2 of a sufiicient thickness has been formed on top of layer 1, by absorption of the moisture contained in the slop, the amount of slop 2 which is still liquid is poured out and the hollow space still left is filled up with slop 3 (steatite), which is now allowed to solidify, whereupon the vane thus formed is burnt or baked. It will be understood, however, that it would also be possible in this manner to provide more than two superposed layers 1, 2, before the inner space is filled up by the material 3 of a high mechanical strength.

It will thus be seen that the blade portion 4 consists mainly of the outer layer of a high resistance against changes of temperature while the share of the material of a higher mechanical strength is gradually increasing towards the root and reaches its maximum thickness at the root portion 5 of the vane where maximum mechanical strength is required.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention and it is intended, therefore, to cover all such changes and modifications in the appended claims.

Having thus described my invention, I claim as new and desire to secure by Letters Patent:

1. A unitary composite ceramic turbine vane of the character described comprising a fired ceramic core of high mechanical strength at elevated temperatures and a substantially continuous surface portion overlying said core and integrally bonded thereto consisting essentially of a fired ceramic material of greater resistance than said core to thermal shocks from abrupt temperature variations.

2. A vane adapted for use in hot gas turbines and the like where it is subject to large mechanical forces and to a widely varying range of temperatures, said vane being formed entirely of ceramic material and having a blade portion formed of ceramic material predominately resistant to high temperatures and to wide variations in temperature, and a root portion formed predominantly of a different ceramic material having greater mechanical strength and stability than said blade portion.

3. A vane adapted for use in hot gas turbines and the like where it is subject to large mechanical forces and to a widely varying range of temperatures, said vane being formed entirely of ceramic material and having a blade portion formed of ceramic material predominately resistant to high temperatures and to wide variations in temperature, and a root portion formed predominantly of different ceramic material having greater mechanical strength and stability than said blade portion, said portions merging smoothly into each other avoiding any sharply defined line of division therebetween.

4. A vane adapted for use in hot gas turbines and the like where it is subject to large mechanical forces and to a widely varying range of temperatures, said blade having a blade portion and a root portion both formed entirely of ceramic material, the outer surface of both portions being formed of a ceramic material comprising silicon carbide and having high resistance to temperature and to temperature change and the inner part of both portions being formed of ceramic material comprising steatitc and having greater mechanical strength and stability than said outer surface.

5. A unitary ceramic vane adapted for use in hot gas turbines and the like where it is subject to large mechanical forces and to a widely varying range of temperatures, said vane having a blade portion and a root portion both formed entirely of ceramic material, the

outer surface of both portions being formed of a ceramic material having high resistance to temperature and to temperature change and the inner part of both portions being formed of ceramic material having greater mechanical strength than said outer surface, the outer portions constituting a greater proportion of the section in the blade portion than in the root portion providing predominant temperature stability in said blade portion and predominant mechanical stability in said root portion.

6. A unitary composite ceramic turbine vane of the character described comprising a blade portion and thickened root portion for mounting said vane in a turbine rotor, a substantially continuous working surface consisting essentially of a fired ceramic material of high resistance to changes of temperatures overlying both said blade portion and said root portion, a core within said surface consisting essentially of a fired ceramic material of higher mechanical strength at elevated temperatures than said surface, said core comprising a preponderantly major part of said thickened root portion and a substantially lesser part of said blade portion.

7. A unitary composite ceramic turbine vane adapted for use in hot gas turbines and the like where it is subject to large mechanical forces and to a widely varying range of temperatures comprising a blade portion and a thickened root portion, an outer working surface consisting essentially of a fired ceramic material of high resistance to changes of temperature overlying both said blade portion and said root portion, a core within said surface consisting essentially of a fired ceramic material of higher mechanical strength at elevated temperatures than said surface material, said core comprising a preponderantly major part of said thickened root portion and a substantially lesser part of said blade portion, and an intermediate transition layer between said outer surface and said core consisting essentially of a fired ceramic material of greater mechanical strength than said surface material but lesser mechanical strength than said core, said layers and said core being integrally bonded together to form said unitary composite vane.

References Cifed in the file of this patent UNITED STATES PATENTS 526,669 McLaughlin Sept. 25, 1894 1,896,123 Schweitzer Feb. 7, 1933 2,058,479 Lysholm Oct. 27, 1936 2,256,479 Holzwarth Sept. 23, 1941 2,277,543 Downs Mar. 24, 1 942 2,288,661 Wadman July 7, 1942 2,297,508 Schutte Sept. 29, 1942 2,431,660 Gaudenzi Nov. 25, 1947 2,479,057 Bodger Aug. 16, 1949 2,502,592 Rieke Apr. 4, 1950 FOREIGN PATENTS 380,391 Italy 1940 574,770 Great Britain Jan. 21, 1946 OTHER REFERENCES Ser. No. 385,334, Schutte (A. P. (3.), published May 25, 1943.

Handbook of Chemistry and Physics, 25th ed., 1941, by Charles D. Hodgrnan and Harry N. Holmes, pub. by Chemical Rubber Publishing C0,, (page 1647 only). 

